Size Selection of Short-necked Clam (Paphia undulata) Dredge in Thai Waters: An Application of Selectivity Model to Improve the Fishery Management

Abstract

The short-necked clam (Paphia undulata) has been a commercially important marine species throughout the Indo-Pacific region for centuries. Recently, the sieve sizes of the short-necked clam dredge still need to be reconsidered by fishery managers and stakeholders to ensure the sustainability of this resource. This study aimed to (i) review the short-necked clam fisheries in Thailand, (ii) apply a parametric selectivity model to the short-necked clam dredge, and (iii) assess the catches to determine the suitable sieve size based on size selectivity, maturity size, and marketable size. This study reviewed and analyzed secondary data, including fishery statistics, fishing gears and operations, short-necked clam dredge experiments, and information on maturity and marketable sizes. Our findings indicated that short-necked clam fishery in Thailand dates back to the 19^th century, evolving from hand-collecting to dredging by fishing vessels both in the Gulf of Thailand and the Andaman Sea. The parametric model was applied to three different sieve sizes (8 mm, 10 mm, and 12 mm) to enhance the precision of size selectivity estimation. The results revealed that the shell length selectivity of the short-necked clam dredge was 26.0 mm, 30.0 mm, and 36.5 mm for the 8 mm, 10 mm, and 12 mm sieve sizes, respectively, with an estimated selection factor of 3.20. The catch assessment demonstrated that a 10 mm or larger sieve size is optimal for reducing the capture of immature and unmarketable short-necked clams and supporting effective fishery management and sustainable resource utilization.